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Lecture 36: Energy Flux in Nature
Reading: Economy of Nature, pp. 127-145.
Equilibrium Theories on Biodiversity Species number on an island may result of an equilibrium (S) between immigration (I) and extinction (E) rates (Ricklefs, 1996, p 561, Fig. 24.11).
The rate of extinctions varies with the size of an island, where small islands have higher extinction rates than do large islands when plotted as a function of the number of species already present. Equilibrium species number on a large island (Sl) is greater than that on a small island (Ss) (Ricklefs, 1996, p 562, Fig. 24.12).
The rate of new species immigration also varies with the distance of an island from the source of new incoming species, where far islands have a slower immigration rate than do near islands when plotted as a function of the number of species already present. Equilibrium species number on a near island (Sn) is greater than that on a far island (Sf) (Ricklefs, 1996, p 562, Fig. 24.13).
Wilson and Simberloff (1970) conducted experiments in which arthopod species immigration and extinction were evaluated on small mangrove islands following the removal of all species. Distance to the mainland was the major difference between these islands. Species immigration occurred most slowly and equilibrium species richness was lowest on the farthest island, as predicted by the equilibrium model (Ricklefs, 1996, p 563, Fig. 24.14).
These models predict species richness dynamics on islands and may apply to island-like patches of habitat such as mountain tops and isolated springs. Existing species richness of amphibians and reptiles on islands in the West Indies (upper graph) and bird species on the Sunda Islands, Malaysia (lower graph) increase with island area (Ricklefs, 1996, p 518, Fig. 22.13). (note that these are log-log plots)
The species saturation of islands in the Pacific Ocean decreases with distance from the source of immigrating species. This graph is for non-marine, resident lowland bird species on islands of the same area (after Begon, Harper, and Townsend, 1990, p 779, Fig 22.10).
The species richness of boreal mammals on mountain top "islands" in the U.S. Great Basin, arthropods on "islands" of marsh grass, and mollusk species in New York lakes (aquatic "islands" in a "sea" of land) also increases with "island" area (after Begon, Harper, and Townsend, 1990, p 770, Fig 22.2)..
Recolonization of new habitat is predicted to yield equilibrium species richness in ecological time. The volcanic explosion at Krakatau (Indonesia) 1883 removed all plants and animals but recolonization began very rapidly afterward and equilibrium species numbers for plants and birds were reached.
An equilibrium species richness can also be predicted for large continents based on rates of speciation and extinction among existing species (Ricklefs, 1996, p 563, Fig. 24.15).
Local conditions determine the shape of these curves and chance (unpredictable) events in the evolutionary process can be important. In evolutionary time (geological time) diversity has generally increased as measured by the number of marine animal families and the number of terrestrial plant species in a given community type (Ricklefs, 1996, p 559, Fig. 24.10). Note that there are long time period with relatively stable numbers of taxa (families or species) and other time periods with increasing (or decreasing) numbers.
Energy Flux in Nature Primary Production (1° P): Sunlight energy capture based on carbon fixation
Secondary Production (2° P): Biomass produced by heterotrophs
Net Primary Production (NPP) Worldwide
Oceans cover approximately 66% of earth surface but account for only 33% of total net primary production. Most primary production in the oceans is in coastal and upwelling zones where nutrients are most abundant (Ricklefs, 1996, p 178, Fig. 8.8 and p 83, Fig. 4.5).
NPP is not spread evenly in all areas of the earth. NPP varies with latitude (see lecture 35 on causes for species richness gradients). All NPP ultimately depends on solar radiation, but solar radiation alone does not determine NPP. Water and nutrients must be available and temperature must be suitable for terrestrial plant growth. Limits on NPP
Perennial grass production in southern Arizona as a function of summer precipitation (Ricklefs, 1996, p 134, Fig. 6.5).
World distribution of annual precipitation (Ricklefs, 1996, p 82, Fig. 4.3).
The relationship between phytoplankton production and inorganic phosphorus concentration is seen in waters off Long Island, NY (collection stations are shown on map). Addition of phosphate or ammonium to water samples from each station indicate that nitrogen is the most important limiting nutrient in these coastal marine ecosystems (Ricklefs, 1996, p 135, Fig. 6.7).
Temperature varies with latitude and that variation creates air circulation cells that influence precipitation patterns. The bar graph shows annual (cm) precipitation (top scale) and the line show temperature as a function of latitude (Ricklefs, 1996, p 81, Fig. 4.2).
Increases in temperature and precipitation both yield increases in NPP (after Begon, Harper, and Townsend, 1990, p 660, Fig 18.8).
Temperature increases cause increases in both GPP and respiration so there is an optimal temperature for NPP and plant growth (after Begon, Harper, and Townsend, 1990, p 661, Fig 18.9).
A total of 30% of terrestrial surface area and 90% of marine surface area have less than 400g/m2/year NPP. This is desert level production. The open ocean is a desert.
Ecosystem types and net annual primary production (Ricklefs, 1996, p 136, Table 6.1).
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